The pathway of formate formation and coenzyme reduction during carbon monoxide respiration in Methanosarcina acetivorans

产甲烷的古细菌被认为是通过一个电子传递链来保存能量，这个电子传递链是由导致甲烷形成的反应（产甲烷）所推动的。在Methanosarcina acetivorans C2A对一氧化碳（CO）的生长过程中，甲烷通过已知的CO2还原途径产生，但在没有任何氢化酶活性的情况下，M. acetivorans如何还原该途径中两个反应所需的辅因子F420尚不清楚。令人惊讶的是，甲基硫化物、乙酸酯和甲酸酯也在羧营养条件下产生。前两种代谢物是如何形成的，是通过我们实验室的遗传和生理分析确定的。然而，甲酸形成的途径（其速度甚至超过甲烷生成的速度）仍不清楚，但甲酸脱氢酶显然不参与其中。本项目的目的是阐明m.a etivorans中CO生成甲酸的途径，在遗传和生化水平上表征所涉及的因素，并表征呼吸链中辅酶F420和辅酶B和辅酶M异二硫化物的还原当量的途径。突变分析和生化技术将被用来实现这一目标。M. acetivorans的CO代谢将作为甲烷菌物种代谢灵活性的范例，这在甲烷菌中是无与伦比的，显然远远超过了教科书上所接受的知识。

Methanogenic Archaea are thought to exclusively conserve energy through an electron transport chain fueled by reactions leading to methane formation (methanogenesis). During growth of Methanosarcina acetivorans C2A on carbon monoxide (CO) methane is generated via the known CO2 reduction pathway but how - in the absence of any hydrogenase activity - M. acetivorans reduces cofactor F420, which is required for two reactions in the pathway, is unknown. Surprisingly, methylsulfides, acetate and formate are also produced under carboxidotrophic conditions. How the former two metabolites are formed was established through genetic and physiological analyses in our laboratory. However, the pathway of formate formation, the rate of which exceeds even that of methanogenesis, remains elusive but formate dehydrogenase is apparently not involved. The aim of the proposed project is to elucidate the pathway of formate formation from CO in M. acetivorans, to characterize the factor(s) involved both on the genetic and on the biochemical level, and to characterize the path reducing equivalents take for reduction of coenzyme F420 and the heterodisulfide of coenzyme B and coenzyme M in the respiratory chain. Mutational analysis and biochemical techniques will be employed to achieve this goal. CO metabolism of M. acetivorans will serve as a paradigm for the metabolic flexibility of Methanosarcina species, which is unsurpassed among methanogens, and apparently far exceeds what is accepted as text-book knowledge.